Vegetable oil widely contains a slight amount of phytosterol such as β-sitosterol, stigmasterol and campesterol in the form of the free-type phytosterol and the ester-type phytosterol.
For example, rape oil contains 0.3˜0.7% of the ester-type phytosterol and 0.2˜0.4% of the free-type phytosterol; corn oil contains 0.3˜0.8% of the ester-type phytosterol and 0.1˜0.4% of the free-type phytosterol; and soybean oil contains 0.1˜0.5% of the ester-type phytosterol and 0.1˜0.4% of the free-type phytosterol.
Recently, a cholesterol-lowering effect due to the phytosterol has been noticed, and water-in-oil (WIO) type emulsion such as fat spread is now commercially available.
However, among phytosterol produced as edibles, the free-type phytosterol is hardly soluble both in water and oil, and the ester-type phytosterol is hardly soluble in water. Some adjustment will be needed in the formulation of foods comprising them.
When compared with the W/O type emulsion such as fat spread, the O/W type emulsion has more problems that a drastic increase in particle size due to aggregation of oil drops and the phase-transition of emulsion will cause reduction in emulsion stability, making it liable to induce the destruction of emulsion during storage, especially under loads such as shaking during distribution or transportation.
Techniques such as those to reduce a ratio of oil phase or to add an emulsifier were tried in order to overcome the above destruction of the emulsion. However, the reduction of the ratio of oil phase would eliminate body taste, and an excess amount of the added emulsifier would deteriorate its taste.
The representative related techniques in the art will be listed as follows.
First, the Japanese Patent Application Publication Hei 11(1999)-506324 (the applicant: Unilever N.V.) discloses an invention relating to fat-based foods defined by their components and contents for the purpose of lowering cholesterol in serum. However, although it discloses butter-like spread, dressing, coffee creamer, and shortening as the examples of the fat-based foods, it does not refer to O/W emulsion that has a stability-related problem It describes that esterification would rather be a non-preferable embodiment (page 14, second paragraphs before Example 1).
Second, the Japanese Patent Application Publication Hei 11 (1999)-146757 (the applicant: Unilever N.V.) discloses an invention relating to a stable aqueous dispersion or suspension and its use for foods, enabling the use of fat/oil having a high melting point such as phytosterol. It also describes that the diameter of the particles of said fat/oil and the amount of an emulsifier should be limited in order to use said fat/oil, and that non-esterified sterol would be most advantageously applied (the paragraph 45).
Third, the Japanese Patent Application Publication Hei 11(1999)-127779 (the applicant: Unilever N.V.) discloses an invention relating to foods containing sterol-containing fat and having a cholesterol-lowering effect. The invention aims at resolving the problems involved in the esterification of the phytosterol that it will reduce the cholesterol-lowering effect in serum, and that it will also need a long time and a high cost for its processes.
Forth, the Japanese Patent Application Publication 2000-102361 (the applicant: McNeil PPC., Inc.) discloses an invention relating to a method for the production of salad dressing containing sterol ester, which is stable even under refrigeration (the paragraph 0001). The invention is characterized by comprising an emulsifier or hydro-colloid, and an inhibitor against crystallization of fat. With respect to the sterol ester, it does not describe or suggest a degree of esterification, but just discloses a supplying amount of P-sitosterol for the purpose of decreasing the amount of cholesterol.
The purpose of the present invention is to provide an O/W type emulsion supplemented with phytosterol, which has a high emulsion stability.